Sarin is a human-made chemical warfare agent classified as a nerve agent and is the most toxic and rapidly acting of the known chemical warfare agents. It is similar to certain kinds of pesticides, called organophosphates, but is much more potent.

Sarin originally was developed in 1938 in Germany as a pesticide.

Sarin is a clear, colourless, and tasteless liquid that has no odour in its pure form. However, sarin can evaporate into a vapour (gas) and spread into the environment.

Symptoms appear within a few seconds after exposure to the vapour form of sarin and within a few minutes and up to 18 hours after exposure to the liquid form.

Symptoms of exposure include:

Runny nose and watery eyes

Small, pinpoint pupils, blurry vision and eye pain

Drooling and excessive sweating

Coughing, tightness in the chest and rapid breathing

Confusion, weakness and drowsiness

Altered heart rate or blood pressure

Sarin is the most volatile of the nerve agents, which means that it can easily and quickly evaporate from a liquid into a vapour and spread.

Syrian government forces have used chemical weapons in their fight against rebels the Israeli military's top intelligence analyst has claimed.

Brigadier-General Itai Brun told a security conference photos of victims showing foam coming out of their mouths and contracted pupils were signs that nerve gas had been used.

"To the best of our understanding, there was use of lethal chemical weapons. Which chemical weapons? Probably Sarin," Brigadier-General Itai Brun said in remarks broadcast on Army Radio.

In a transcript of Brun's speech provided by the Israeli military, he said forces loyal to Syrian President Bashar al-Assad were behind the attacks on "armed (rebels) on a number of occasions in the past few months".

The Syrian government and rebels last month accused each other of launching a chemical attack near the northern city of Aleppo.